The present invention is related to roller clamps for regulating the flow of a fluid through an elastically deformable tubing, particularly for infusion/transfusion devices in the medical field.
More particularly, the invention is directed to a roller clamp of the type comprising a generally channel-shaped body having two lateral walls and a bottom wall defining a clamping surface along at least part of which a central longitudinal groove is formed having an initial end and a terminal end and having a cross section which is decreasingly variable from said initial end towards said terminal end, and a roller rotatably supported by said lateral walls of the body and longitudinally displaceable in a guided fashion within said body substantially parallel to said clamping surface of the bottom wall so as to clamp in use an elastically deformable tubing fitted through the body between said bottom wall and said roller.
Roller clamps of the above referenced type are known for instance from U.S. Pat. No. 4,725,037 and U.S. Pat. No. 5,014,962.
When using such roller clamps the flow of the fluid along the elastically deformable tubing is adjusted by varying the longitudinal positioning of the roller along the clamping surface of the body bottom wall. The condition of minimum or null flow corresponds to positioning of the roller in correspondence of the terminal end of the longitudinal groove formed along the clamping surface of the bottom wall, whilst the condition of maximum flow corresponds to positioning of the roller in correspondence of the initial end of the longitudinal groove. This is evidently due to the fact that the section of the tubing, which is clamped and pressed between the roller and the portions of the clamping surface of the body bottom wall comprised between the central longitudinal groove and the lateral walls of the body itself, defines a restricted central passage for the fluid whose size depends upon the depth of the central longitudinal groove: evidently, the smaller the section of the central longitudinal groove is, the smaller is the cross section of such a passage, and vice-versa. In other words, as the roller is positioned more and more towards the terminal end of the longitudinal groove, the tubing is more and more strictly clamped and thus subjected to a more and more relevant elastic deformation. Since the tubing is normally made of thermoplastic material, or anyway of a material whose deformation takes place under constant volume, and since the space available for deformation thereof is limited on one side by the clamping surface of the bottom wall, on the other side by the roller, and sideways by the lateral walls of the body, the more the roller is shifted towards the terminal end of the central longitudinal groove, the more the space available for elastic deformation of the tubing is reduced. As a consequence the reaction to squeezing which is applied by the tubing against the roller progressively increases towards the terminal end of the longitudinal groove, which may require a remarkable effort to be applied by the operator to displace the roller towards and from said terminal end. This effort may quite become excessive and jeopardize the clamp operating capability.
This problem is particularly critical in case of tubings having relative thicker and thus harder walls.